As a process for flattening a semiconductor wafer such as a silicon wafer is conventionally adopted a chemical mechanical polishing (CMP) process (for example, see the Patent Document 1).
According to the CMP process, a polishing pad is retained on a machine platen and an object to be polished, such as a silicon wafer, is retained on a polishing head, and the polishing pad and the object to be polished, which are being pressurized, are slid over each other while slurry is continuously supplied thereto so that the object is polished.    PATENT DOCUMENT 1: 2000-334655 of the Japanese Patent Applications Laid-Open